That's impressive work, given that he began tweeting only a year and a half ago, averages fewer than two messages per day, writes many of them in Spanish and was off the radar while sidelined for seven months after Wimbledon last year. His total is 400,000 more than that of Serena Williams, who is No. 2 among tennis players.

Here's the breakdown on Nadal's Twitter reach:

https://twitter.com/tennistweetscom/status/317704709563641857

https://twitter.com/tennistweetscom/status/317705150020075522

Here's Rafa's first tweet, sent on Aug. 2, 2011:

https://twitter.com/RafaelNadal/status/98375699534053377

His four million Twitter followers complement a huge profile on Facebook, where he has 11.5 million fans. Taken as a whole, Nadal has the biggest following on all English social media. Roger Federer, who is not on Twitter, ranks second thanks to 12.5 million Facebook fans. On the women's side, Maria Sharapova leads the pack with 9.7 million Facebook fans and a slow-growing Twitter following of nearly 170,000.